The invention relates to a module for generating UV light for irradiating a substrate.
Discharge lamps for generating radiation, in particular for the targeted generation of UV radiation, are already known from the prior art. The doping of the gas filling, in order to attain a targeted effect on the shape of the emission spectrum and thus to optimize the lamp for different applications, is also described in various publications. Such lamps can be constructed as low-pressure emitters, medium-pressure emitters, or high-pressure emitters, and via the pressure under which the discharge takes place during operation, both the spectrum and the power are influenced with respect to the volume of the discharge.
However, even with optimally doped discharge lamps operating in the optimum pressure range, only a portion of the emitted radiation is used for the desired process, since spectra of discharge lamps always also contain components in the visible or in the infrared range, and because a portion of the power heats up the envelope tube and this tube itself radiates in the far infrared. The portions of the spectrum of the emitted radiation that are harmful or undesired for the process are often removed from the spectrum of the overall radiation by a filter.
Such discharge lamps or the discharges used as radiation sources radiate in all spatial directions, so that at least in the radial direction only a negligible dependency of the emitted intensity on the angle between the lamp and substrate exists.
In order to attain the most efficient use possible of the emitted radiation, among other things the radiation emitted uniformly in all directions from the lamp is deflected by reflectors onto, for example, a substrate. Here, spectrally wide-band, specular reflectors do not provide good efficiency (that is, high reflectivity) for UV, because metals exhibit a high absorption and ceramics are either still transparent or likewise exhibit a high absorption. Specular reflection is understood to be reflection on an essentially smooth surface, whereby the angular information of the radiation is preserved.
Since simple material boundary faces other than in the visible (Ag, Al) or infrared (nearly all metals) are not available as efficient reflectors, dielectric reflectors are used made of transmissive materials having layer sequences of varying indices of refraction. Such reflectors have only a limited bandwidth within which they actually reflect. Therefore, they can also be used as a filter. The production of such reflectors is expensive, because a plurality of different layers must be deposited on a high-quality, polished carrier.
Because the reflective area of a dielectric reflector depends on the angle under which the light is incident on the reflector, such reflectors must be designed for the geometric situation under which they are operated. In order to obtain a reasonably homogeneous reflectivity across the surface being used, this must be arranged at a constant angle relative to the radiation source. The reflector must be mounted at a not too small distance from the light source, because the radiation emitted from the lamp is not from a punctiform origin, but instead originates from the entire surface area of the discharge and is thus incident at different angles on the reflector, but for a high efficiency, great variations in angles at which the radiation is incident on the reflector are not permissible.
The continuous operation of such reflectors is expensive, because these usually must be cooled—they are optimized for high reflectivity in the UV or VIS and therefore strongly absorb outside of their reflective, spectral ranges. Compact installations are therefore typically water-cooled, which is associated with high costs and with expensive constructions.
Modules for UV or VIS radiation, that is, housings in which radiation sources, reflectors, and optionally shutters are housed, always consist of a plurality of components and typically require water for cooling the reflector and the shutter. Only units of very low power can have an air-cooled construction. Such a module is described, for example, in International patent application publication No. WO 2005/105448 as prior art. German utility model DE 20 2004 006 274 U1 gives an example of the difficulties of how a flashlight can be extremely compactly and easily constructed. For this purpose, an external reflector must be selected. The power of the lamp is only very low, so that the use of very large dimensioned cooling by air prevents an overheating of the lamp and the reflector. From this it follows that the system has disproportionately large dimensions, in comparison with the dimensions of the actual light source, and thus consists of a plurality of single parts.
Decisive for a long service life and thus high utility for the user of UV lamps is furthermore the temperature of the pinching of the emitter and the lamp tube. The temperature of the pinching should not exceed 300° C., but the lamp tube can exhibit significantly higher temperatures, so that additional measures are necessary for the separate cooling of the pinched regions for lamps of higher power densities.
German patent document DE 33 05 173 shows how it is possible to design purely air-cooled devices by use of complex flow channels and the use of lamps having low power densities. The power density is defined as the power/length of the discharge.
The above-mentioned modules are all rather complex and expensive in their configuration or can emit only low power/device volume.